Floquet-Mode TWPA Critical-Current Taper for Low-Loss Broadband Gain
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Solution Overview
Problem
Current Floquet mode traveling wave parametric amplifiers (TWPAs) face challenges in achieving near-ideal quantum efficiency, large bandwidth, and sufficient power handling for the readout of multiple qubits due to material loss and limited fabrication techniques.
Innovation Solution
A Floquet mode TWPA design featuring a plurality of stages with nonlinear elements, such as Josephson junctions, and low-loss capacitors, where the critical current of the nonlinear elements varies monotonically from the input to the output, minimizing reflections and backward amplification, and utilizing planar or parallel plate capacitors to reduce material loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If Floquet mode TWPAs are designed with greater electrical length to provide broadband amplification, then bandwidth is improved, but material loss increases leading to limited quantum efficiency
Solution Approach 1:
The patent applies parameter changes by systematically varying the critical current of Josephson junctions along the amplifier length according to a specific profile (monotonically decreasing from input to output). This parameter variation enables the amplifier to achieve broadband operation while maintaining low loss, as the gradual change in nonlinear element strength optimizes the Floquet mode coupling across a wide frequency range without requiring excessive electrical length.
Solution Approach 2:
The patent implements local quality by creating spatial variation in the nonlinear element characteristics along the amplifier structure. Specifically, the critical current is engineered to decrease monotonically from the input to the output, creating different local amplification properties at different positions. This local differentiation allows the amplifier to handle a broad spectrum of frequencies efficiently while minimizing overall material loss through optimized local coupling conditions.
2Ease of manufacture
If conventional TWPAs use constant critical current nonlinear elements, then fabrication is simplified, but reflections and backward amplification increase reducing quantum efficiency
Solution Approach 1:
The patent resolves this contradiction by implementing parameter changes in the critical current of nonlinear elements along the amplifier length. Instead of using constant critical current, the design employs a monotonically decreasing profile from input to output. This parameter variation suppresses reflections and backward amplification by creating impedance matching conditions that prevent signal bounce-back, thereby achieving high quantum efficiency (>90%) while remaining fabricable using standard techniques.
Solution Approach 2:
The patent applies the dynamics principle by introducing a dynamic (spatially varying) critical current profile rather than a static constant value. The critical current is engineered to change continuously along the amplifier length, creating a dynamic structure that adapts to different signal conditions at different positions. This dynamic design suppresses unwanted reflections and backward amplification while maintaining manufacturability through systematic fabrication approaches.
3Reliability
If Josephson parametric amplifiers use nonlinear resonators for near-ideal quantum efficiency, then quantum efficiency is improved, but bandwidth and dynamic range are limited
Solution Approach 1:
The patent applies mechanics substitution by replacing the resonant mechanical-like oscillation approach of conventional JPAs with a traveling wave approach based on Floquet modes. Instead of relying on a single resonant frequency, the invention uses a continuous spectrum of Floquet modes that can be excited along the transmission line, enabling broadband operation. The nonlinear Josephson elements are arranged to support traveling wave amplification rather than resonant oscillation, achieving both high quantum efficiency and wide bandwidth.
Solution Approach 2:
The patent implements periodic action through the use of periodically modulated nonlinear elements along the transmission line. The Josephson junctions are arranged with periodic variation in their critical currents, creating a periodic structure that supports Floquet mode amplification. This periodic modulation enables the amplifier to operate across a broad frequency range by exciting multiple Floquet sidebands, thereby achieving both high quantum efficiency and expanded bandwidth beyond what single-resonator JPAs can provide.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The design achieves near-ideal quantum efficiency, expanded bandwidth, and improved power handling, enabling the simultaneous high-fidelity readout of tens to hundreds of qubits, while reducing material loss and enhancing directionality and stability compared to conventional TWPAs.
Implementation Method 1
The nonlinear elements may be Josephson junctions, or a combination of series and/or parallel Josephson junctions
Implementation Method 2
The Floquet mode TWPA comprises a plurality of stages, where each stage is made up of a nonlinear element and a capacitor
Data Source
AI summary
A Floquet mode traveling wave parametric amplifier (TWPA) is disclosed. The Floquet mode TWPA comprises a plurality of stages, where each stage is made up of a nonlinear element and a shunt capacitor. The nonlinear elements may be Josephson junctions, or a combination of series and/or parallel Josephson junctions. The Floquet mode TWPA is designed such that the critical current of the nonlinear elements in each stage is not constant. In some embodiments, the ratio of the largest critical current to the smallest critical current in the Floquet mode TWPA is at least 2:1. In some embodiments, the nonlinear elements with the largest critical current are disposed at or near the input or output of the amplifier. In this way, reflections and backward amplification may be minimized. Further, the TWPA is formed using planar capacitors on a high resistivity substrate, or using low loss parallel plate capacitors.